1. Field of the Invention
The present invention pertains to a barrier layer structure deposited on a semiconductor substrate, wherein the barrier layer structure comprises oxygen to improve the performance of the barrier layer, and to the method used to deposit this barrier layer structure on the substrate.
2. Brief Description of the Background Art
As is well-known in the semiconductor device art, conventional integrated circuit processing steps can cause silicon atoms to diffuse from single-crystal silicon into a metal electrode of pure aluminum to such a depth as to short out a shallow p-n junction in the silicon; this phenomenon is known as junction spiking. Variance occurs during the etching of contacts, and when a contact is over-etched, an increase in spiking is observed. Over-etching provides more area for silicon and aluminum interdiffusion to occur at the bottom of a contact.
To elevate the contact bottom and thus prevent the interdiffusion of adjacent layers of aluminum and silicon and the resultant junction spiking at the bottom of a contact, barrier layers were introduced between the silicon and the overlying aluminum layer prior to aluminum filling and planarization. The most commonly used barrier layer for aluminum contacts is titanium nitride. The titanium nitride may be used alone or in combination with titanium, which may be used to decrease the resistance of the contact. Titanium nitride and titanium layers are typically deposited at the bottom and on the sidewalls of a contact via using physical vapor deposition (PVD). PVD techniques are well-known in the art.
Ion Metal Plasma (IMP) sputter deposition is a recently developed method of PVD which provides uniform barrier layer bottom and sidewall coverage in small contacts. IMP sputter deposition of titanium nitride barrier layers is disclosed in U.S. application Ser. No. 08/511,825 U.S. Pat. No. 5,962,923 of Xu et al., assigned to the assignee of the present invention.
In particular, "IMP" sputtering refers to deposition sputtering, where sputtered target material is passed through an ionization means, such as an inductively coupled RF source, to create a high density, inductively coupled RF plasma between the sputtering cathode (target) and the substrate support electrode. This ensures that a higher portion of the sputtered emission is in the form of ions at the time it reaches the substrate surface. Although not required, the substrate toward which the sputtered ions are moving is typically biased to attract the incoming ions.
IMP sputter-deposited titanium nitride films having low stress and providing high bottom coverage in high aspect ratio features are disclosed in U.S. application Ser. No. 09/003,014, filed Jan. 5, 1998. Although IMP sputter-deposited titanium nitride provides excellent bottom coverage for small contacts, as contact size decreases, increasingly rigorous process conditions (for example, higher process temperatures) are needed, which may cause the titanium nitride layer to fail as a barrier layer. One method of improving the effectiveness of the titanium nitride barrier layer is by oxygen stuffing. The presence of the oxygen atoms in the titanium nitride matrix disrupts channel formation through which mobile silicon atoms at the bottom of the contact can travel.
While oxygen stuffing of sputter-deposited titanium nitride films does prevent the migration of silicon upward from the bottom of the contact, it also introduces additional problems: the oxygen can migrate through the thin titanium nitride barrier layer to the titanium wetting layer on the sidewalls of the contact via, contaminating the titanium wetting layer and forming a layer of titanium oxide which can interfere with the filling of the contact via. Additionally, during filling of the contact, the oxygen can react with the aluminum fill as it flows over the barrier layer surface, resulting in the formation of an undesirable layer of aluminum oxide on the interior surface of the contact via. Aluminum oxide at the bottom of the contact layer increases contact resistivity and aluminum oxide on the sidewalls of the contact via prevents aluminum from flowing easily over the surface of the sidewalls and can cause void formation within the contact.
Therefore, a method of depositing an effective oxygen-containing barrier layer at the bottom of a contact to prevent spiking, while minimizing the oxygen content on the contact via sidewalls to permit complete filling of very small contacts, would be highly advantageous.